Anesthesiologists often use nerve stimulation to localize a desired nerve or nerves prior to administration of a local anesthetic (Von Perthes is generally credited with providing the original description of using peripheral nerve stimulators for regional anesthesia in 1912). Nerve stimulation typically utilizes electric current to elicit visible muscle twitches as a result of stimulation of the nerve or nerves to thereby confirm proximity of the needle to the nerve. This technique relies generally upon two phenomena. First, that many nerves, when properly stimulated by electric current, will cause a corresponding substantially predictable movement (such as a twitch) of a portion of the patient's body (in particular, muscle contractions resulting from stimulation of the nerve(s)). Second, that the amount of electric current required to cause the desired muscle movement will vary predictably with distance between the tip of the needle that sources the electric current and the nerve.
Stimulation typically begins with a higher intensity current (such as, for example, 1.5 to 2.0 milliamperes). Upon observing the anticipated muscle movement (thereby indicating that the needle is positioned within a given distance from the nerve, the current is reduced and the process repeated until the current has been reduced to a predetermined range (such as 0.2 to 0.5 milliamperes), thereby indicating that the needle is within a clinically relevant distance from the nerve to best facilitate the anesthesia of the nerve after introduction of a local anesthetic via the needle. When conducting this kind of procedure, it is important to avoid contacting or piercing the nerve with the needle as this can cause injury to the nerve. Generally, stimulation of the nerve with low current intensity (e.g., less than 0.5 milliamperes) indicates an intimate needle-nerve relationship and advancing the needle closer to the nerve after the stimulation is achieved at less than 0.5 milliamperes caries a risk of contacting or piercing the nerve.
The procedure typically requires two people. One person handles manipulation of the needle and observes the patient's response while the second person operates the remote peripheral nerve stimulator apparatus and visually monitors the current delivered. In particular, the latter person controls the amount of current being applied via the needle (as well as other parameters that pertain to the current being provided). For a variety of good reasons (e.g., lack of space, difficulty of placing the stimulator on the patient, preserving the sterile field, and so forth) the remote peripheral nerve stimulator itself is usually located at a certain distance away from the patient and the person manipulating the needle. The person manipulating the needle therefore must manage a consider degree of cognitive loading; they must physically manipulate the needle in a careful fashion while also observing the anticipated muscle response and also while remaining cognizant of the present amount of current being delivered via the needle. This person typically keeps verbally informing the person performing the block of the intensity of the current being delivered, so that the person performing the block does not have to frequently shift their gaze from the procedure to the display on the nerve stimulator and thus be distracted from the procedure. This can still require, in many instances, a considerable amount of frequent gaze shifting and/or repositioning by the person performing the procedure, particularly when the current gauge (or other indicator) on the nerve stimulator apparatus is located some distance away from the needle operator. Not surprisingly such physical and mental challenges give rise to a situation where errors are more likely to occur. These errors can be a direct result of the need for gaze alteration and distraction and typically include unwanted needle movement during gazing, which in turn may result in failure to anesthetize the nerve or piercing the nerve when the needle is inadvertently pushed deeper or pulled back more superficially from its original location. In addition, even when a single person performs the block and manipulates the stimulator at the same time (rare, but possible by use of a remote controller of the nerve stimulator, such as a foot pedal), the need to constantly shift one's gaze between the patient, needle, procedure, and the display on the nerve stimulator can still be very distracting.
The above approach is encumbered with other concerns and issues as well. For example, it is possible for the needle operator to insert the needle into the patient and to begin to manipulate it before the nerve stimulator apparatus operator has begun to provide current to the needle. It is also possible for the supply of electric current to fail during the procedure, such that the needle operator continues to manipulate the needle while unaware of this condition. Such conditions can result in discomfort and/or harm to the patient and/or an unsuccessful procedure. As another example, it is possible for the cord that couples the nerve stimulator apparatus to the needle to be improperly coupled to one or the other device or to become partially or fully disconnected during the procedure. This can result in either a complete failure to deliver current to the needle or a partial failure (where, for example, only a portion of the indicated current is actually being delivered to the needle). It is also possible for miscommunication to occur between the operator of the needle and the person operating the nerve stimulator, resulting in decisions made by the person operating the needle being inconsistent with the actual present electric current intensity.
Nerve stimulator devices typically have at least one indicator to represent the operational status of the machine. Light emitting diode meters, liquid crystal displays, flashing diodes, gauges of various types, and audible beeps, for example, have all been used to monitor current availability and/or to signal a malfunction. Such remotely placed indicia, unfortunately, doesn't always adequately serve the operator who manipulates the needle. Tight operating quarters and physical remoteness of the nerve stimulator machine can make it difficult for the needle operator to accurately view such visible displays, as can the required physical positioning and posturing of the needle operator during a given procedure. Furthermore, audible alerts are easily confused with other ordinary sounds of the operating theater (for example, patients receiving a nerve block are usually monitored by pulse oximetry which is also typically accompanied by an audible beeping sound).
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.